The present invention provides an improvement pertaining to an apparatus intended for use with the dynamic balancing of rotating workpieces, such as armatures. Balancing operations involving rotating workpieces generally require that some, if not all, of the following steps be performed:
picking up the workpiece from a feed conveyor and transferring it to a balance measurement station; PA1 measuring the amount and angle of unbalance at the measurement station; PA1 indexing the workpiece to a first correction plane; PA1 performing a weight correction by weight removal or weight addition at the first correction plane; PA1 indexing the workpiece to a second correction plane if two-plane balancing is required; PA1 performing a weight correction at the second correction plane, if necessary, by weight addition or weight removal; PA1 auditing the workpiece correction and balance; PA1 transfer of the workpiece from the audit apparatus to the exit conveyor.
Currently, two distinct types of devices commonly offer the capability of performing these balancing steps. These devices are generally referred to as a master station apparatus and a multi-station apparatus. Balancing machines based on the master station concept involve a transfer system which brings the workpiece to one machine at one location. The single master machine performs all individual balancing measurement and audit functions and all correction functions as necessary without any transfer of the workpiece between functions. Balancing machines based on the multi-station concept spread the balancing measurement and audit functions and correction functions to separate machines located at distinct stations so that each step of the balancing cycle is performed at a separate station. A transfer system picks the workpiece up at each station and delivers it to the next station in line.
The multi-station apparatus is capable of performing at high production rates, primarily as a result of the fact that each of the individual stations are capable of performing their individual tasks at the same time. Further, even though the multi-station machine is complex as a whole, each individual machine component or station is relatively simple in design and less costly than a master station machine. The multi-station apparatus does, however, have disadvantages due to the overall complexity of the machine and the potential for duplication of expensive components at the individual stations. For instance, two balance measurement stations are generally required--one for the original balancing measurement step and the second for the audit balance measurement step; two weight correction and clamping stations are necessary following the original balancing measurement station for correction in the first plane and the second, if two plane correction is required, following the first plane correction station; numerous indexing mechanisms to maintain proper alignment of the workpiece between stations; and numerous transfer mechanisms and grippers located between each of the component stations. Add to this extensive amount of duplicated componentry the necessary electrical components, controls, computers and programming requirements and it is quite obvious that multi-station devices can sometimes be undesirably complex and expensive.
Another complexity involving multi-station devices lies in the necessity of maintaining a known angular orientation of a workpiece as it is transferred between stations. Typically, the workpiece index angle must be closely held within tolerance between at least the measurement or audit stations and the correction stations or correction inaccuracies may occur. For instance, during a complete balancing cycle, the workpiece is received from an in-feed conveyor and placed on a balance measurement machine. The amount and angle of unbalance is determined by the measurement machine and the workpiece is then indexed to the proper angle for the correction step. The indexed workpiece is then transferred to a weight correction machine and a calculated amount of material is either removed from or added to the workpiece at the proper angle orientation. In some instances of two-plane correction, the workpiece is again indexed and may be transferred to a second weight correction machine. After the weight correction steps, the workpiece is transferred to a second measurement machine and audited. At this point, the corrected workpiece is either rejected or accepted. Thus, it can be seen that the indexing of the workpiece and maintenance of its angle orientation is critical between balancing, correction, auditing and re-correction steps.
The multi-station device generally requires that most automated production lines be unidirectional. Therefore, once in the loop, the workpiece must continue through the entire cycle. If a workpiece is found to be in tolerance at the first measurement station and does not need correction, it must still continue the cycle through all the stations. Further, if the workpiece is not in balance after going through the entire balancing sequence, it must usually be removed from the exit conveyor and brought to a manual machine for further balancing. The out-of-tolerance workpiece cannot be recycled through the automated line because no memory is retained which accounts for previous corrections made to the part. Therefore, on re-correction, the part could potentially receive a correction operation at the position of the original correction.
The master station balance and correction apparatus sometimes presents a desirable alternative to the multi-station apparatus. Duplication of machine components is eliminated and the transfer of workpieces between stations, with the exception of the loading and unloading of the workpiece, is eliminated. Because there is no transfer operation between stations, there is no need for complex orientation and indexing maintenance equipment. Further, in the master station apparatus, workpieces that do not require correction can be immediately returned to the conveyor, thus saving cycle time and idle time. Another desirable characteristic of the master station apparatus is the ability to remeasure the balance and make additional corrections to the workpiece without removal of the workpiece from the machinery. In this instance, the computer retains previous correction memory for a given workpiece and the workpiece can be effectively fine-tuned in correction without difficulty. Finally, the master station device generally has less initial cost than the multi-station balancers. However, to equal the production rate of a multi-station balancer and correction device, three or four master station devices may be needed. Thus, overall costs potentially remain high. The use of a multiple number of master station devices does provide versatility and the advantage that if one of the master station devices breaks down the others will continue production whereas if one station in a multi-station machine breaks down all production for the entire line is halted.
Production speed is always an area of concern when inserting a balancing and correction station into an assembly or production line. The speed with which workpieces can be transferred between conveyors and various work stations comes under continuous scrutiny. Two transfer systems are most commonly employed in balance measurement and correction operations. The walking beam transfer system employs a pivoting articulating beam to move or "walk" workpieces in a single direction. The walking beam system is not commonly employed with balancing and correction operations because it has minimum flexibility and can only move in one direction for a fixed distance and is difficult to incorporate into congested areas. The more commonly used transfer system is generally referred to as "pick and place" transfer technology.
The pick and place type transfer system commonly includes one or more vertical up/down slide members mounted on a single carrier plate. The carrier plate is usually mounted on a single slide unit designed for horizontal linear transfer or for non-linear rotational transfer. Each up/down slide member includes a set of grip mechanisms which are spaced so as to allow two workpieces to be held side-by-side without interference. The carrier plate with the slide members and two grip members travels on the single slide unit between the various balance measurement and correction stations. Pick and place transfer systems of this type commonly use valuable cycle time in two detrimental ways: since the grip members are mounted side-by-side, the transfer apparatus must traverse the distance separating the grip members in order to position one or the other set of grip members over a single station. For instance, in high speed automated lines having total balance measurement and correction cycles times per workpiece of between six and twelve seconds, this transfer time can add approximately 1 to 1.1 seconds to a cycle. Further, once one set of grip members is in position over the station, the grip member is moved down or up on its slide to "pick" a workpiece out of the station. The other set of grip members must then move down or up to "place" a new workpiece into the same station after the transfer time. Each down/up motion takes approximately 0.8 to 1 seconds to "pick" and "place" workpieces, thereby adding approximately 1.6 to 2 seconds of cycle time to the 1 to 1.1 seconds of transfer time. In high speed automated lines, this cycle time presents a target for improvement.
It can be seen that the multi-station balancing and correction devices provide for a high production rate but provide very little versatility and are prone to circumstances wherein the entire line may be shut down due to the failure of one component of the device. The master station balancing and correction devices cost less than the multi-station device on a per unit basis yet have greatly diminished production capacity when compared with the multi-station apparatus. Thus, it is an object of the present invention to provide a balancing and correction device having the simplicity in components and versatility of production of the master station apparatus and yet produce the higher production rate available with the multi-station apparatus.
Another object of the invention is to provide a differentiation between the balance measurement and audit functions and the correction functions within a single device or machine.
Yet another object of the invention is to provide a single device having a balance measurement and audit modular station and a correction modular station.
A further object of the invention is to provide a balancing and correction machine wherein the transfer mechanism between the balance measurement and audit modular station and the correction modular station allows work to be done on workpieces at both stations simultaneously.
Yet another object of the invention is to optimize transfer time between stations and therefore produce the least amount of transfer time impact on overall cycle time.
Another object of the invention is to provide for a correction detection for workpieces to determine where previous corrections were made on a workpiece prior to providing additional corrections to the workpiece.
A final object of the invention is to maintain speed of operation of the balancing machine in keeping with constant activity at the slowest cycle step.